We live in a world awash with foreign substances, some inanimate and others, living microbes, in soil, water, and air that are potentially inimical to human health. Throughout evolution, deep seas and high peaks have long provided niches for these substances that are harsh yet permissive for the human species to both adapt to as well as to exploit not only by overwhelming them but at times by profiting from them and by yielding profit in return. Plants and animals, humans among them, for example, have had to cope with bacteria and parasites from the beginning stages of multicellular evolution due to the simple fact that they were here first. Successful adaptation to these foreign agents comprises the classic expressions of protective immunity....